The present invention relates to a device and a method for manufacturing electronic devices containing at least one chip fixed to a support.
In certain fields, including that of smart cards, it is necessary to effect the mounting of a microcircuit or chip on a relatively thin and flexible support. In the case of smart cards, it is necessary on the one hand for the presence of the chip not to cause an excessive thickness beyond a threshold established by international standards (currently fixed at 50 xcexcm) and on the other hand for the mounting of the chip to be sufficiently secure to allow durable use even when the card is subjected to relatively high bending and twisting stresses.
In a conventional manner, the creation of an excessive thickness is avoided by housing the chip in a cavity provided for this purpose in the thickness of the support.
FIG. 1 schematically shows a known example of mounting a chip 6 on a support 2 intended to constitute a smart card. The chip 6 is housed almost entirely in a cavity 3 so that its thickness is included within that of the support 2. The chip 6 has a set of connecting pads 5 on the edges of its surface turned towards the outside of the cavity 3. These pads 5 are connected to respective contacts 7 on the support by wires 9. The contacts 7 can be situated at the bottom of the cavity, or at an intermediate level in a recessed area 11 around the cavity, as in the example illustrated. These contacts 7 are in their turn electrically connected to contact areas 13 intended to allow an ohmic connection with a card reader. These contact areas 13 are housed entirely in the recess 11 so that their thickness is also contained within that of the support 2.
To protect the whole, a coating of protective material 15 is formed, covering the entire area occupied by the cavity 3, the wires 9 and a portion of the internal edges of the contact areas 11.
This conventional technique suffers from several drawbacks. Firstly, the operation consisting in electrically connecting the connecting pads 5 of the chip 6 to the contacts 7 requires the use of very fine and delicate wires 9, thus forming fragile points. Moreover, the operations of soldering these wires 9 requires a significant amount of tooling and a not insignificant amount of time.
Moreover, the formation of the cavity 3 requires a machining step which is both expensive and weakening for the card.
It should also be noted that this technique based on the integration of a chip in a cavity in a support is difficult to use when it is necessary to connect together several components, for example several chips or other passive or active elements on the same support.
In addition, it is important to design methods which are compatible with automated tooling for mass production, allowing high rates of attaching and welding chips.
In the light of these problems, the present invention proposes a method for mounting at least one microcircuit in the form of a chip on a support, characterised in that it includes, for the chip or chips, the following steps:
a) providing a chip produced as a very thin semiconductor having at least one interconnection point in the form of a contact pad made from weldable material, said pad having a welding face substantially in the same plane as at least one of the faces of the said chip;
b) providing, at the support, at least one interconnection area intended to be welded with a corresponding contact pad on the chip;
c) placing the welding face of the contact pad or pads on the said chip opposite the corresponding interconnection area or areas on the support; and
d) welding the contact pad or pads on the said chip with the corresponding interconnection area or areas on the support.
The present invention advantageously uses the technology of chips produced in a very thin substrate, as described notably in the patent document WO-A-9802921 in the name of Kopin. This technology notably makes it possible to dispose chips having a thickness of 10 microns, or even very substantially less than this thickness.
Advantageously, the interconnection area of the support is produced on a portion of a surface of a face of the support situated in the general plane of this face. In other words, no cavity or recess is created for accommodating the thickness of this interconnection area. Because of this, the interconnection area and also the chip project with respect to the overall plane of the face on which they are situated. This arrangement is possible, by virtue of the invention, because a chip especially configured according to the definition in paragraph a) above is provided.
Preferably the contact pad or pads are produced in aluminium.
Likewise, it is also possible to produce the interconnection area or areas in aluminium.
The method according to the invention lends itself notably to welding by thermocompression or ultrasound.
According to a first embodiment of the invention, the contact pad or pads of the chip pass through the thickness of the chip so as to have a surface accessible on each of the faces of the chip.
This arrangement notably makes it possible to perform the welding step by transmission of energy through the pad or pads in the direction of the thickness of the chip. In other words, the energy for the welding is applied to the face of the contact pad situated opposite to the welding face.
According to one advantageous aspect of this embodiment, a protective substrate which holds the chip is also provided at step a). The welding step can then be performed after the removal of this substrate from the chip.
According to a second embodiment of the invention, a protective substrate with a first face which holds a set of chips is also provided at step a).
Before the welding step, cuts are made around at least one chip on the protective substrate, with a depth of cut which reaches at least the first face of the substrate. After the welding step, the support with its welded chip or chips is separated from the protective substrate. The fact that the cuts have previously been made around the chip makes it possible to remove it in its cut form. It is then possible to perform the aforementioned cuts in the form of notches which pass only partially through the thickness of the protective substrate. In this case, the substrate for all the chips on a wafer remains whole, which facilitates the removal of the chips after welding.
Advantageously, according to this second embodiment, at least when the support is separated, the protective substrate is held so as to enable the chip to be removed by peeling when the support is separated.
The substrate can be held by the interposing of an adhesive layer between a second face thereof, opposite to the first, and a base.
According to a variant of this second embodiment, the depth of cut completely passes through the protective substrate. This arrangement is possible when the protective substrate can be fixed firmly to its base, for example by means of the aforementioned adhesive layer.
The present invention also relates to a device, such as a smart card, having at least one microcircuit in the form of a chip mounted on a support and connected to at least one interconnection area for the support, characterised in that the chip or chips have at least one contact pad having a surface for contact with a corresponding contact area on the support, the contact surface being, at one face of the chip, opposite the contact area.
Advantageously, the contact surface of the contact pad is substantially on the same plane as the face of the chip opposite the said interconnection area.
Preferably, the interconnection area of the support is produced on a portion of a surface of a face of the support which is situated in the overall plane of this face.
The contact pad or pads can be produced from aluminium.
According to a first embodiment of the device, the contact pad or pads pass through the thickness of the chip.
Advantageously the chip has an excess thickness relative to the overall plane of the face of the support on which it is attached equal to or less than 50 microns.